1. Field of the Invention
The present invention relates to a method of manufacturing an optical fiber base material that may manufacture a highly reliable optical fiber and a method of manufacturing an optical fiber using the same.
2. Description of Related Art
As one of methods of manufacturing an optical fiber base material, an inside mounting method is known. In the inside mounting method, a glass tube of which both end portions are horizontally fixed and supported is heated while rotating about its axis. At the same time, a raw material gas is supplied to a through-hole of the glass tube, and a glass layer is laminated on the inner wall of the glass tube based on the raw material gas. Then, after a plurality of glass layers are laminated, the entire glass tube collapses, and hence an optical fiber base material is manufactured. As one of the inside mounting methods, an MCVD (Modified Chemical Vapor Deposition) method may be exemplified. In the MCVD method, the glass tube is heated from the outside thereof when the raw material gas is supplied to the through-hole of the glass tube. By the heating, soot which is generated from the raw material gas is deposited, and the deposited soot (fine glass particles) becomes a glass layer by the heat.
However, since the glass tube is heated while both end portions are fixed, the glass tube may be entirely bent in an arch shape or may be locally bent. The arch-like bending is different from the warpage caused by the own weight of the glass tube, and maintains the glass tube to be bent in a specific direction. Accordingly, when such a bending occurs, a whirling causing the eccentric rotation of the glass tube occurs with the rotation. The whirling also occurs even in a case where the glass tube is locally bent. Particularly, when the glass tube is long, the warpage amount caused by the own weight increases, and hence there is a tendency that the bending more easily occurs.
When the whirling caused by such a bending of the glass tube occurs, the temperature distribution in the circumferential direction of the glass tube increase with the rotation of the glass tube, and the thickness of the laminated glass layer may be easily different partially in the circumferential direction. For this reason, the eccentric amount of the core glass body in the manufactured optical fiber base material increases, and in the optical fiber manufactured by using the optical fiber base material, the eccentric amount of the core exceeds the allowable amount, which may degrade the reliability. Accordingly, it is preferable to suppress the warpage of the glass tube which causes the bending of the glass tube. In the case of the MCVD method, since the glass tube is heated from the outside, a portion close to the heat source and a portion away from the heat source are generated. Accordingly, the temperature distribution particularly increases, and hence there is a tendency that the eccentric amount of the core glass body in the optical fiber base material further increases.
As a method of suppressing the bending of the optical fiber base material, there is known a method of manufacturing an optical fiber base material disclosed in Japanese Patent Application National Publication No. 2005-520776. In the method of manufacturing the optical fiber base material, an auxiliary support member is used which supports the outer peripheral surface of the glass tube from the downside at the middle position of the glass tube of which both end portions are fixed. Then, the glass tube is heated while rotating in a state that the glass tube is supported by the auxiliary support member. Since the warpage of the glass tube during the heating in this way is suppressed, the above-described bending is suppressed and the eccentricity of the core glass body is reduced.